Autonomic impairment is minor in idiopathic amyotrophic lateral sclerosis (ALS) and Alzheimer's-type dementia (D) and is usually not marked in Parkinson's disease. The autonomic status of Guamanian parkinsonism (P), ALS, and parkinsonism-dementia complex (PDC) is essentially unknown. We therefore evaluated the autonomic nervous system in Guamanian D, ALS, P, and PDC. Cardiovagal, adrenergic, and postganglionic sudomotor functions were quantitated in 16 patients and 14 paired household controls. Patients comprised PDC (N = 11), D (N = 2), P (N = 2), and ALS (N = 1). Autonomic deficit was expressed on a composite autonomic scoring scale (CASS) and its subsets that corrects for the effects of age and gender. CASS severity was rated from 0 to 10 and the maximal subset scores were 3, 3, and 4 for postganglionic sudomotor, cardiovagal, and adrenergic deficits, respectively. CASS scores for mild, moderate, and severe autonomic failure are 1 to 3, 4 to 6, and 7 to 10, respectively. Symptoms were scored by an Autonomic Symptom Profile (ASP). The affected patients were older than and had a sex distribution different from paired controls (64.2 +/- 8.0 versus 53.1 +/- 13.5; p < 0.01; male/female = 9/7 versus 2/12; p = 0.045). CASS scores were markedly increased over paired controls (6.2 +/- 2.3 versus 1.9 +/- 1.3; p < 0.001), and involvement was generalized by system. There were deficits in sudomotor, cardiovagal, and adrenergic function. Orthostatic hypotension occurred in 6 of 16 patients and 2 of 14 paired controls. Guamanian patients had more autonomic dysfunction than non-Guamanian Parkinson's disease. ASP scores were higher in patients than controls and regressed with CASS. These differences persisted when corrected for the confounding effects of age, gender, and diabetes. We conclude that Guamanian patients have autonomic failure to a greater extent than non-Guamanian Parkinson's disease or ALS. This autonomic failure suggests multisystem autonomic involvement similar to but less severe than in multiple system atrophy.